Fix stop_neutron metadata agent function

Currently, stop_neutron fails in Jenkins because it kills itself.
This patch ensure we kill only neutron metadata agent, and not the awk
process in itself.

Change-Id: I25d1d90e002fa9eb3c5bc366cc74cb70a2daa69f
Closes-bug: #1269982
Signed-off-by: Emilien Macchi <emilien.macchi@enovance.com>
Merge "Fix stop_neutron metadata agent function"